Combined heat engines and heat pumps are generally well known like constructions based on the Vuillemier cycles as one example.
Most thermodynamic cycles (e.g., Carnot, Rankine, Brayton, Stirling, etc.) are based on reversible processes. Each cycle usually includes four such processes. A reversible process is by definition lossless. A thermodynamic cycle that consists of reversible processes is lossless. Thermodynamic losses in a combined reversible cycle are external, and the thermodynamic efficiency of the combined cycle is based on external losses and depends on how the heat is delivered from the outside and delivered to the outside of the combined cycle. The practical usefulness of combined cycles is dependent on the real efficiency of included sub-processes.
FIGS. 1 and 2 show the basic trilateral cycles and Brayton cycles and/or processes that function as heat engines and heat pumps. FIG. 1 shows a temperature-entropy (TS) diagram for a typical trilateral cycle that has an ascending upside and a horizontal bottom. The trilateral cycle of FIG. 1 also works in conjunction with a gradient heat source and a constant temperature (isothermal) heat sink, and operates as a motor when the cycle moves in the clockwise direction.
In the trilateral cycle of FIG. 1, 1-2 represents a process that increases the temperature of the working fluid slightly without changing the entropy, 2-3 represents an isobaric, increasing temperature gradient heat transfer process, 3-4 represents an adiabatic expansion process, and 4-1 represents an isothermal, isobaric heat transfer process (i.e., heat transfer to the outside; e.g., as a result of a phase change from gas to liquid). The heat added to the cycle from a heat source is Qin=Q2-3. The heat delivered from the cycle to a heat sink is Qout=Q4-1. The mechanical power added to the cycle is W1=W1-2. The mechanical power produced by and/or transferred within the system is W2=W3-4.
Since the cycle is reversible, the diagram of FIG. 1 also shows a trilateral heat pump cycle with a constant temperature heat source and a gradient heat sink when operating in the opposite direction (counter clockwise) as a heat pump. In the reverse cycle, 4-3 represents an adiabatic compression, 3-2 represents an isobaric, decreasing temperature gradient heat transfer process, 2-1 represents a pressure recovery process, and 1-4 represents an isothermal and isobaric heat transfer (e.g., phase change from liquid to gas). The heat added to the cycle from a heat source is Qin=Q1-4. The heat delivered from the cycle to a heat sink is Qout=Q3-2. The mechanical power added to the cycle is W1=W4-3. The mechanical power delivered from the cycle is W2=W2-1. U.S. Pat. Appl. Publ. No. 2011/0139407 discloses such a cycle for thermoelectric energy storage in liquids.
FIG. 2 shows a TS diagram for a typical Brayton cycle that has an ascending upside and a descending downside. The Brayton cycle of FIG. 2 includes a gradient heat source and a gradient temperature heat sink, and operates as a motor in the clockwise direction. In the Brayton cycle of FIG. 2, 5-6 represents an adiabatic compression, 6-7 represents an isobaric, increasing temperature gradient heat transfer, 7-8 represents an adiabatic expansion, and 8-5 represents an isobaric, decreasing temperature gradient heat transfer process. The heat added to the cycle from a heat source is Qin=Q6-7. The heat delivered from the cycle to a heat sink is Qout=Q8-5. The mechanical power added to the cycle is W1=W5-6. The mechanical power delivered from the cycle is W2=W7-8.
Since the cycle is reversible, the diagram of FIG. 2 also shows a Brayton heat pump cycle with a gradient temperature heat source and a gradient heat sink, operating as a heat pump in the opposite (counter clockwise) direction. In the reverse cycle, 8-7 represents an adiabatic compression, 7-6 represents an isobaric, decreasing temperature gradient heat transfer process, 6-5 represents an adiabatic expansion, and 5-8 represents an isobaric, increasing temperature gradient heat transfer. The heat added to the cycle from a heat source is Qin=Q5-8. The heat delivered from the cycle to a heat sink is Qout=Q7-6. The mechanical power added to the cycle is W1=W8-7. The mechanical power delivered from the cycle is W2=W6-5. U.S. Pat. Appl. Publ. No. 2010/301614 discloses such a cycle for thermoelectric energy storage in solid materials.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.